This invention relates to valve shut-off mechanisms for automatically operating a gas valve or the like to shut off the flow of fluid in a pipeline in response to an earthquake.
Vibration sensitive devices are known which are designed to respond to earthquake vibrations of a predetermined magnitude in order to shut off a valve in a gas conduit or the like. Such devices function as a safety mechanism for reducing the possibility of explosion due to ruptured gas connections downstream of the valve and within a building structure, such as a private dwelling, an apartment building or an office building. Many different designs for such devices have been proposed, of which the disclosures of U.S. Pat. Nos. 2,615,460 and 3,791,396 are believed to be representative.
Known earthquake responsive valve shut-off mechanisms typically suffer from several disadvantages. Some are difficult to install or reset after being tripped, or both; others may only be installed in a horizontal position in order to be fully operative. Some are only responsive to earthquake vibrations of massive proportions; others are sensitive to seismic vibrations unrelated to earthquakes, such as vibrations caused by passing trucks, locomotives or other heavy land vehicles, or frictional forces resulting from mechanical loading; still others can be accidentally tripped by a prowling animal or small child. Some known devices are only compatible with certain types of valve mechanisms, and many require removal of the valve from the gas conduit for installation. Still others require modification of an existing valve installation, and many can only be installed by skilled technical personnel. Many devices are also unprotected against enviromental elements and thus must be tested at frequent intervals to ensure their continued operability. Efforts in the past to design an earthquake responsive valve shut-off mechanism devoid of the above disadvantages have not met with success.